1. Field of the Invention
This invention relates to a method of manufacturing an Alxe2x80x94Mgxe2x80x94Si series alloy plate excellent in thermal conductivity and intensity.
2. Description of Related Art
Generally, Japanese Industrial Standards (hereinafter referred to as xe2x80x9cJISxe2x80x9d) A5052 aluminum alloy is used as high intensity aluminum materials for heat exchanger parts, metallic base printed circuit boards, cutting members, etc. However, JIS A5052 aluminum alloy is inferior in thermal conductivity by 30% or more as compared with pure aluminum. On the other hand, pure aluminum having high thermal conductivity is extremely low in strength and inferior to JIS A5052 aluminum alloy in cutting processability. This pure aluminum requires removal of burrs after cutting processing, resulting in poor finished surface appearance.
Furthermore, Alxe2x80x94Mgxe2x80x94Si series alloy is also used as aluminum material of high intensity in which fine Mg2Si particles are precipitated uniformly to improve the strength. The fine Mg2Si precipitation can be obtained by heat treatment, which improves strength and recovers toughness by hardening and annealing the alloy after cold rolling. Heating the alloy in general rolling process does not cause uniform and fine Mg2Si precipitation, but merely causes independent precipitation of Mg and Si, resulting in insufficient strength improvement.
Thus, under the present circumstances, it is additionally required to perform heat treatment after cold rolling, resulting in an increased step, which causes an increase in the manufacturing cost. Furthermore, in cases where a thin plate having a thickness of 0.1 mm or the like is manufactured from heat treatment type alloy such as Alxe2x80x94Mgxe2x80x94Si series alloy, since it was common to subject the alloy plate of 1 mm thickness or less to solution treatment in a continuous annealing furnace, it was difficult to increase the cold working rate. As a result, it was difficult to obtain high hardness.
Japanese Unexamined Laid-open Patent Publication No. H6-272001 discloses a method of manufacturing an Alxe2x80x94Mgxe2x80x94Si series alloy plate in which hot rolling conditions are specified. This technique intends to restrain big and rough precipitation from being generated during hot rolling in order to perform short-time solution treatment after cold rolling, and does not intend to promote fine Mg2Si precipitation during the rolling process.
It is an object of the present invention to provide a method of manufacturing aluminum alloy with outstanding thermal conductivity and hardness in fewer steps.
According to the present invention, a method of manufacturing an Alxe2x80x94Mgxe2x80x94Si series alloy plate excellent in thermal conductivity and hardness, includes the steps of: preparing Alxe2x80x94Mgxe2x80x94Si series alloy ingot consisting essentially of Si:0.2-0.8 wt %, Mg:0.3-0.9 wt %, Fe:0.35 wt % or less, Cu:0.20 wt % or less and the balance of aluminum and inevitable impurities; homogenizing the alloy ingot; subjecting the alloy ingot to rough hot rolling to obtain a roughly hot rolled plate; subjecting the roughly hot rolled plate to finish hot rolling to obtain a finished hot rolled plate; and subjecting the finished hot rolled plate to cold rolling, wherein one of the rough hot rolling is controlled such that material temperature immediately before the one of the rough hot rolling is from 350 to 440xc2x0 C., cooling rate between the one of the rough hot rolling and rough hot rolling subsequent thereto is 50xc2x0 C./min or more, material temperature immediately after the one of the rough hot rolling is from 250 to 340xc2x0 C. and plate thickness immediately after the one of the rough hot rolling is 10 mm or less, and wherein the cold rolling is controlled such that rolling reduction is 30% or more.
It is preferable that Si content of the Alxe2x80x94Mgxe2x80x94Si series alloy ingot is from 0.32 to 0.60 wt % and/or Mg content of the Alxe2x80x94Mgxe2x80x94Si series alloy ingot is from 0.35 to 0.55 wt %.
It is preferable that the material temperature immediately before one of the rough hot rolling is from 380 to 420xc2x0 C., and/or the plate thickness immediately after one of the rough hot tolling is 8 mm or less.
It is also preferable that the rolling reduction of the cold rolling is 50% or more.
Furthermore, it is preferable to further perform last annealing at 180xc2x0 C. or below after the cold rolling
The present invention will be detailed as follows. In the method of manufacturing an Alxe2x80x94Mgxe2x80x94Si series alloy plate excellent in thermal conductivity and hardness, the significance and reasons for the limitation of each element of the target Alxe2x80x94Mgxe2x80x94Si alloy composition will be explained as follows.
Mg and Si are essential elements for giving strength to the alloy. If Mg content is 0.3 wt % or less and/or Si content is 0.2 wt % or less, sufficient strength cannot be obtained. On the other hand, if Mg content exceeds 0.9 wt % and/or Si content exceeds 0.8 wt %, the rolling load in the hot rolling will increase, which causes a deterioration of productivity and necessitates trimming of the rolled plate before the finish rolling because of large cracks. The desirable lower limit of Mg content is 0.35 wt %, and the desirable upper limit thereof is 0.55 wt %. On the other hand, the desirable lower limit of Si content is 0.32 wt %, and the desirable upper limit thereof is 0.60 wt %.
Too much Fe and Cu causes a deterioration of corrosion resistance, resulting in an alloy plate of no practical use. Therefore, it is necessary to regulate the content of Fe and Cu such that Fe content is 0.35 wt % or less and Cu content is 0.20 wt % or less. The desirable Fe content is 0.25 wt % or less, and the desirable Cu content is 0.10 wt % or less.
The alloy composition falling within the aforementioned range causes outstanding thermal conductivity equivalent to pure aluminum.
In the method according to the present invention, fine Mg2Si particles can be precipitated uniformly by applying rolling under the prescribed conditions after the homogenization. As a result, effects equivalent to effects obtained by solution treatment and quenching can be obtained.
The conditions of the homogenization are not specifically limited. It is preferable to perform the homogenization for 2 hours or more at 500xc2x0 C. or above in accordance with a conventional method.
In the rough hot rolling, effects equivalent to effects obtained by quenching can be obtained by the temperature reduction while rough hot rolling under the predetermined temperature conditions in any rough hot rolling pass. Therefore, the material temperature immediately before the rough hot rolling is required to fall within the range of from 350 to 440xc2x0 C. which can retain the dissolved state of Mg and Si like in solution treatment. If the material temperature is below 350xc2x0 C., Mg2Si becomes big and rough precipitation at this time, and thus the subsequent quenching effect cannot be obtained. Furthermore, since the material temperature is low, the rolling nature of the subsequent rough hot rolling pass deteriorates remarkably, the material temperature immediately after the rough hot rolling pass becomes too low, resulting in a deterioration of the surface quality. On the other hand, if the material temperature exceeds 440xc2x0 C., the material temperature will not drop enough immediately after the rough hot rolling, causing insufficient quenching effects. The preferable lower limit of the material temperature immediately before the rough hot rolling is 380xc2x0 C., and the preferable upper limit is 420xc2x0 C. Furthermore, in order to obtain the quenching effects, it is required to control such that the cooling rate between subsequent rough hot rolling passes is 50xc2x0 C./min and that the material temperature immediately after the hot rolling pass falls within the range of from 250 to 340xc2x0 C. In order to control the material temperature immediately after the hot rolling pass so as to fall within the aforementioned range, forced cooling such as high-pressure shower water cooling may be performed immediately after the rough hot rolling. Furthermore, it is preferable that the rough hot rolling velocity is 50 m/min or higher. Furthermore, in order to obtain cooling effects equivalent to quenching between the rough hot rolling passes, it is necessary to control such that the plate thickness immediately after the rough hot rolling becomes 10 mm or less because of the following reasons If the thickness exceeds 10 mm, it is difficult to cool the plate to a temperature sufficient for quenching even if an additional water-cooling process is performed. The preferable plate thickness is 8 mm or less.
Generally, although the aforementioned rough hot rolling will be performed 10 times (passes) or more, the aforementioned rough hot rolling pass under the aforementioned conditions in order to obtain the quenching effects may be performed at any rough hot rolling pass. However, since it is required to make the plate thickness immediately after the rough hot rolling 10 mm or less, the aforementioned rough hot rolling is usually performed at the last rough hot rolling pass or at the rough hot rolling pass immediately before the last rough hot rolling pass. However, in cases where the aforementioned rough hot rolling is performed at a rough hot rolling pass other than the last rough hot rolling pass, it is required to perform the rough hot rolling subsequent to the pass at the material temperature of from 250 to 340xc2x0 C. If the material temperature is below 250xc2x0 C., the load of rolling becomes larger. As a result, it becomes hard to perform the rough hot rolling because of the large load and the surface changes in quality, e.g., the surface corrosion due to the reaction of aluminum and moisture.
The conditions of the final hot rolling performed after the rough hot rolling, such as the result temperature and/or the rolling velocity, are not specifically limited because solution treatment and quench treatment have been already performed by the preceding rough rolling. Accordingly, the final hot rolling may be performed depending on the plate thickness by a conventional method.
In the cold rolling, in order to obtain the predetermined hardness by work hardening, it is necessary to control such that the rolling reduction is 30% or more. When the rolling reduction is 30% or more, the hardness of 200 N/mm2 or more which is equal to the hardness of JIS A5052 aluminum alloy can be obtained. A desirable rolling reduction is 50% or more.
Furthermore, if it requires, the last annealing of the cold rolled alloy plate may be performed at 180xc2x0 C. or below. By performing the heat treatment at such a low temperature, the age hardening of the alloy plate will be executed to further increase the hardness and the elongation. Furthermore, mechanical characteristics will also be stabilized. The most preferable annealing temperature is from 130 to 150xc2x0 C.
Since the target Alxe2x80x94Mgxe2x80x94Si series alloy to be manufactured in accordance with the manufacturing method according to the present invention consists essentially of Si:0.2-0.8 wt %, Mg:0.3-0.9 wt %, Fe:0.35 wt % or less, Cu;0.20 wt % or less and the balance of aluminum and inevitable impurities, the obtained Alxe2x80x94Mgxe2x80x94Si series alloy is excellent in thermal conductivity. The method of manufacturing an Alxe2x80x94Mgxe2x80x94Si series alloy plate according to the present invention includes the steps of: homogenizing the Alxe2x80x94Mgxe2x80x94Si series alloy ingot; subjecting the alloy to rough hot rolling to obtain a roughly hot rolled plate; subjecting the roughly hot rolled plate to finish hot rolling to obtain a finished hot rolled plate; and subjecting the finished hot rolled plate to cold rolling, wherein one of the rough hot rolling is controlled such that material temperature immediately before one of the rough hot rolling is from 350 to 440xc2x0 C., cooling rate between one of the rough hot rolling and rough hot rolling subsequent thereto is 50xc2x0 C./min or more, material temperature immediately after one of the rough hot rolling is from 250 to 340xc2x0 C. and plate thickness immediately after one of the rough hot rolling is 10 mm or less, and wherein the cold rolling is controlled such that rolling reduction is 30% or more. Accordingly, during the rough hot rolling, it is possible to obtain effects equivalent to the effects obtained by solution treatment and quench treatment. Furthermore, still higher hardness can be obtained by the cold rolling at the high rolling reduction. Therefore, without performing heat treating at another process other than rolling process, an alloy plate having high thermal conductivity and high hardness can be manufactured, and a large cost reduction can be attained. Furthermore, since the Alxe2x80x94Mgxe2x80x94Si series alloy plate manufactured by the method shown here has good cutting ability, when cutting of this alloy plate is performed, post processing, such as deburring, become unnecessary and a cost reduction can also be attained. Furthermore, since the thermal conductivity of Alxe2x80x94Mgxe2x80x94Si series alloy is good, the alloy plate having high thermal conductivity and high hardness can be manufactured by the aforementioned method.
Furthermore, in the aforementioned Alxe2x80x94Mgxe2x80x94Si series alloy ingot composition, in cases where Si content is from 0.32 to 0.60 wt % and/or Mg content is from 0.35 to 0.55 wt %, the obtained alloy plate is excellent especially in hardness.
Furthermore, in cases where the material temperature immediately before one of rough hot rolling is from 380 to 420xc2x0 C., sufficient quenching effects can be obtained while maintaining the rolling nature.
Furthermore, in cases where the plate thickness immediately after one of the rough hot rolling is 8 mm or less, the plate can be fully cooled between the rough hot rolling passes. Thus, sufficient quenching effects can be obtained.
Furthermore, in cases where the rolling reduction at the cold rolling is 50% or more, the strength improvement effect due to work hardening will be remarkable.
By performing the last annealing at the temperature of 180xc2x0 C. or below after the cold working, the hardness of the alloy plate can be further improved, the elongation can also be increased and the mechanical characteristics can be stabilized.